The invention relates to apparatus for automated handling and transferral of thin substrates, and more particularly to thin semiconductor wafers of the type from which a very large plurality of individual electronic micro circuits or components are made using well-known coating, masking and impurity introduction techniques. Such wafers are highly fragile and easily damaged, due to their thinness (of the order of 10-20 mils), large diameter (2 to 5 inches), and highly polished faces, which can be rendered useless for device fabrication by any of many kinds contamination, abrasion, or damage. Thus extraordinary precautions in handling are needed from the very beginning, and in particular it is highly desirable to minimize transferal of the wafers by hand. As the wafers are processed through a large succession of processing stations, implementing for example the above-mentioned techniques, they become ever more valuable, the need to avoid damage and contamination becomes even more imperative, while the cumulative risk of damage steadily increases.
Early handling techniques have included tweezers and vacuum wands and at best merely minimized the need for personnel to touch the wafers. Later attempts to more or less automate the handling of wafers through the necessary processing stations have included a large variety of expedients such as rotary carousels, carrier sleds or platens with endless conveyor belts, linear air bearings or tracks, vibratory tracks, and peripheral clip supports of various kinds. Also, apparatus has tended to be oriented either to batch processing of a plurality of wafers at a station at one time, or to single processing of individual wafers at a particular station at one time. While all of the foregoing have their advantages in certain applications, many have been too complex, not reliable enough in preventing damage or contamination, lacking in compatibility with apparatus of transport or processing stations, subject to difficulty in initially unloading or later unloading, and not well suited to transferal of wafers into and from processing stations requiring a vacuum chamber and the attendant load locks.
The batch type wafer handling apparatus has been further open to objection as inherently subjecting a large plurality of wafers to the risk of a defect or contamination in the process at each station, or in transit between stations, and posing a difficult load/unload bottleneck, particularly when moving the entire batch into and from a vacuum chamber environment. On the other hand, the single processing of individual wafers also has the disadvantage of maximizing the need for increased manual handling, especially in the initial loading and unloading, slowness of overall processing, and complexity or unreliability in interfacing through load locks. The repeated removal and insertion of wafers from and into cassettes required by such individual processing, typically done by a tongue member extending into the cassette and below the wafer to be moved, with the wafers typically oriented horizontally, magnifies the risk of damage and contamination. The associated conveyor belts and platens, or air or vibratory tracks, along with the horizontal placement of the wafers thereon, provide still further opportunity for abrasions. Further, such belts, tracks, platens, and cassettes require elaborate load lock provisions and/or wafer transfer mechanisms to transfer wafers into processing stations wherein a vacuum chamber must be utilized.
Accordingly, an object of the invention is to provide an improved substrate or wafer handling system for automatically moving wafers from a loading or other station individually into a processing station.
Another object of the invention is to provide an improved automated wafer handling system accepting a cassette of vertically oriented wafers and repetitively feeding indvidual ones of said wafers from said cassette into a processing station, and returning same to said cassette.
A still further object of the invention is to provide an improved wafer support and transport means to enable automatic and repetitive moving of individual wafers into and from load locks into, through and between processing stations while minimizing damage and contamination of wafers.
Yet another object of the invention is to provide an improved minimal volume wafer load lock and feeding system therefor for automatically and repetitively moving individual wafers into and from a vacuum chamber processing station with enhanced reliability and speed.